A satellite communication system occasionally experiences conditions which cause the system to provide inferior service to system users. These conditions can include, for example, high traffic congestion on system links and holes in the system's communication coverage area. Other conditions which negatively impact service might include inefficiently routed information and high service costs.
In a satellite communication system, one or more satellites act as system access points which provide communication channels to ground facilities (e.g., gateways and subscriber units) within the system's coverage area. Where a satellite system is experiencing unusually high levels of traffic on the communication links within the system, the satellite system might be forced to refuse service to some users, terminate ongoing service for other users, or inefficiently route traffic through the system. Overly-congested links, thus, can significantly impact the quality of service provided by a satellite system.
Holes in a satellite system's coverage area also can negatively impact service provided. A system's coverage area defines the communication range of the system. If a ground facility is outside the coverage area, the system is unable to communicate with the ground facility. Some satellite systems have coverage areas which normally encompass the entire surface of the earth. Other satellite systems have coverage areas which only partially cover the earth.
During normal operations, a satellite system's coverage area is defined by the number of system satellites, their angles of elevation and altitudes, and the types of antennas which they employ. Occasionally, a system malfunction or planned satellite outage can affect a system's coverage area. For example, where a satellite is damaged and is unable to provide access into the system for a ground facility within its normal coverage area, an outage condition is likely to result. The outage condition typically continues until the satellite is repaired, replaced, or another satellite's coverage area encompasses the ground facility. The area within which the satellite system is unable to communicate during normal operations or as a result of an outage condition is referred to herein as a "coverage hole".
Prior art systems do not provide hand-off procedures which enable a second satellite system temporarily to provide communication services for a first satellite system. Thus, what is needed is a method and apparatus which enable a first satellite system temporarily to hand-off communication links to a second satellite as a result of conditions (e.g., overly-congested links or coverage holes) which cause the first satellite system to provide less-than-optimal communications service.